Not Applicable
1. Field of the Invention
The present invention is directed generally to transmission systems and components. More particularly, the invention is directed toward thermo-stabilization and transmission systems and components utilizing thermo-stabilization, and methods of thermo-stabilization.
2. Background of the Invention
The continued growth in traditional communications systems and the emergence of the Internet as a means for accessing data has accelerated demand for high capacity communications networks. Telecommunications service providers, in particular, have looked to wavelength division multiplexing (WDM) to increase the capacity of their existing systems to meet the increasing demand.
In WDM transmission system, pluralities of distinct information signals are carried using electromagnetic waves having different wavelengths in the optical spectrum, typically using infrared wavelengths. Each information carrying wavelength can include multiple data streams that are time division multiplexed (xe2x80x9cTDMxe2x80x9d) together into a TDM data stream or a single data stream.
The pluralities of information carrying wavelengths are combined into a multiple wavelength, xe2x80x9cWDMxe2x80x9d, optical signal that is transmitted in a single waveguide. In this manner, WDM systems can increase the transmission capacity of existing space division multiplexed (xe2x80x9cSDMxe2x80x9d), i.e., single channel, systems by a factor equal to the number of wavelengths used in the WDM system.
Communications systems, particularly WDM systems, include many temperature sensitive components and assemblies which must be thermo-stabilized for proper operation. For example, lasers, which are typically used in transmitters and amplifiers, as well as in other components, often must be maintained within a temperature range for proper operation. Furthermore, Bragg gratings, which can be used in most components in an optical system, particularly transmitters, receivers, add/drop devices, combiners, and distributors, require thermal stabilization for proper operation. Some components are always thermo-stabilized at a single temperature or temperature range. Other components are thermo-stabilized at any of two or more temperatures or temperature ranges, depending on the particular function to be performed.
Temperature sensitive components and assemblies are often thermo-stabilized using thermo-electric devices along with associated control circuits. One type of prior art thermo-electric assembly is illustrated in FIG. 9. That circuit uses linear regulation, in the form of variable resistance which is controlled by a controller, to control the current to the thermo-electric device. That design is inefficient, often resulting in efficiencies around 60% at high loads and less than 10% at light loads. Furthermore, that design does not provide a mechanism to switch the direction of current through the thermo-electric device, thereby limiting the thermo-electric device to either cooling only or heating only, but never cooling under some conditions and heating under others.
Another prior art control circuit is illustrated in FIG. 10. It uses four switches in an H-bridge configuration and is controlled by a controller. The switches are driven by variable duty cycle pulses at high frequency (typically in a range between about 50 kHz and about 500 kHz) to control the current through the thermo-electric device. That circuit is more efficient than the linear circuit, particularly at light loads, but it still has high losses due to switch capacitance. Furthermore, that design includes two L-C elements to filter and smooth the signal around the thermo-electric device. Those elements are bulky, result in additional power loss, and result in a relatively slow response time.
Yet another disadvantage of the prior art is that temperature of the device is typically determined indirectly by measuring the temperature of or within a chamber in which the device is located. That measurement, however, is not necessarily an accurate measurement of the temperature of the device. In particular, the fiber connected to the device conducts heat to and from the device, thereby affecting the temperature of the device (heat may also be transferred to and from the device by other paths). As a result, prior art thermo-stabilization systems which attempt to maintain a constant temperature within the chamber do not maintain a constant temperature of the device if the ambient temperature varies from the desired temperature of the device. In particular, the temperature of a device varies significantly with ambient temperature when using a prior art system of maintaining a constant chamber temperature. Such variations degrade the performance of the system and, in the case of a wavelength division multiplexed system, require more bandwidth for each channel in order to accommodate the variations caused by ambient temperature fluctuations. As a result, the total number of channels and the overall performance of the system may be decreased.
The development of higher performance communication systems depends upon the continued development of higher performance components and subsystems for use in the system. It is, therefore, essential that optical systems be developed having increased performance capabilities to meet the requirements of next generation optical systems. Accurate, fast, and efficient thermo-stabilization is essential for high performance systems and components.
The apparatuses and methods of the present invention address the above need for improved thermo-stabilization.
One embodiment of the present invention includes a thermo-electric assembly, including a thermo-electric device, and a comparator responsive to a difference between a temperature of a device to be thermo-stabilized, or a chamber containing the device, and a set point temperature for the device or chamber to be thermo-stabilized, having a variable hysteresis, and having an output terminal controlling the current direction through the thermo-electric device. The thermo-electric device may also include a power converter providing variable current to the thermo-electric device, which is controlled by the comparator. The thermo-electric device may further include a processor controlling the variable hysteresis of the comparator.
In another embodiment of the present invention, the comparator is eliminated and the processor includes computer readable code which, when executed by the processor, causes the processor to be responsive to a difference between a temperature of a device to be thermo-stabilized and a set point temperature for the device to be thermo-stabilized, to have a variable hysteresis, and to control current through the thermo-electric device.
In another embodiment of the present invention the ambient temperature is used to dynamically vary the temperature of the chamber in which the device is located.
The present invention also includes optical systems including components and assemblies according to the present invention.
The present invention also includes a method of controlling temperature of a device. One embodiment of the method includes determining the temperature of the device, comparing the temperature of the device to a desired temperature for the device, and heating and cooling the device according to a difference between the temperature of the device and the desired temperature of the device and according to a variable hysteresis loop. The method may also include heating the device by passing current in a first direction through a thermo-electric device without changing direction of the current through the thermo-electric device. The method may also include cooling the device by passing current in a second direction, opposite the first direction, through the thermo-electric device without changing direction of the current through the thermo-electric device. The present invention also includes a method which compensates for temperature variations caused by the ambient temperature and dynamically adjusts the temperature of the chamber.
The optical systems, components, and methods of the present invention provide the increased speed, efficiency, stabilization, and accuracy necessary for transmission systems. These advantages and others will become apparent from the following detailed description.